Field Transmitter: Temperature sensor

Field Transmitter: Temperature sensor Solutions from Texas Instruments

Design Considerations
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Design Considerations

Temperature sensors are used to measure temperature and have a wide range of uses in industrial, commercial applications. Temperature measurements are made using RTD (Resistance Temperature Devices), Thermistor or Thermocouple.

RTD and Thermistor utilize the property of Change in Resistance according to temperature to measure voltage drop across the element and calculate the temperature. A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference, known as Seebeck effect. Ambient temperature is added to this calculated temperature difference to measure actual temperature. The process of measurement of Ambient Temperature is known as cold junction compensation.

Temperature transmitters are of two types. The conventional Field Transmitters working as a part of Industrial control loop that are line or loop powered and the Wireless or Handheld temperature sensors that are battery powered.

Excitation Technique: RTDs and Thermistors being passive elements need a current excitation source to make measurements. Highly stable and accurately matched current sources with low drift are critical to making 3 wire RTD measurements. TI’s temperature sensor front-ends have high precision on-chip current sources. Accurate measurement of the ambient temperature for Cold Junction compensation in Thermocouple measurements can be made using the high accuracy on chip temperature sensor. Thus the TI analog front-end for temperature measurement is a single chip solution that provides all aspects of signal conditioning needed for RTD, Thermistor and Thermocouple measurements.

Signal Conditioning/Signal Acquisition and Processing: The output range of the temperature sensor is very small and thus the signal needs to be amplified before processing to prevent introduction of errors. The signal chain has to handle the small signal accurately in presence of noise. TI’s temperature sensor front-ends have an input multiplexer, high impedance PGA and high resolution sigma-delta modulator all integrated into a single chip. The low noise, chopper stabilized PGA provides the versatility of scaling the gain as needed in accordance with how small or large the output from the sensor is. High end products also have integrated features for system diagnostics and fault monitoring. A further level of system calibration could be implemented in the MCU.

Interface and Communication: Traditional analog (4 - 20mA) interface remains the popular choice for industrial control and sensor applications. The other popular protocols include HART, Profibus and IO-Link. TI's IO-Link interface products have integrated regulators and diagnostic outputs. In addition, wireless options based on IEEE 802.15.4 protocols are becoming more prevalent. TI is committed to provide solutions for both traditional and emerging industrial interfaces.

Power Management: The Field Transmitter can be powered in one of three ways. Line powered transmitters are commonly powered by voltage rails of 12V, or 24V. Loop powered transmitters are powered by the 4-20 mA loop. Such transmitters require extremely low power architectures as the entire solution has to be powered off the loop. TI provides high efficiency Step Down converters with low quiescent current and low output ripple appropriate for Line and Loop powered transmitters. Battery powered transmitters powered can be designed using TI's low power Buck and Buck-Boost converters. The DC/DC buck converters offer over 95% efficiency over a wide battery voltage range, even with input voltage down to 1.8 volts extending battery life. Special Buck-Boost converters generate a stable required output voltage and supply constant current for over- and under-input voltage conditions and support various battery configurations.

Application Notes (8)

Title	Abstract	Type	Size (KB)	Date	Views
A Glossary of Analog-to-Digital Specifications and Performance Characteristics (Rev. B)		PDF	425 KB	09 Oct 2011	77661
Example Applications For Temperature Measurement Using the ADS1247 and ADS1248	Read Abstract	HTM	8 KB	13 Jan 2011	2628
Low-Cost Noise-Immune Isolated Thermocouple Signal Processor	Read Abstract	HTM	8 KB	08 Jan 2007	918
Getting the most out of your instrumentation amplifier design		PDF	177 KB	10 Oct 2005	1813
Practical Technique for Minimizing the Number of Measurements in Sensor Signal	Read Abstract	HTM	9 KB	28 Jun 2005	709
Interfacing the ADS1251/52 to the MSP430	Read Abstract	HTM	8 KB	08 Mar 2005	978
MSP430F42x Single-Chip Weight Scale	Read Abstract	HTM	8 KB	15 Nov 2004	1389
Thermistor Temperature Transducer to ADC Application	Read Abstract	HTM	8 KB	22 Sep 2000	772

Selection and Solution Guides

Selection Guides (5)

Title	Type	Size (KB)	Date	Views
Power Management Solutions for Ultra-Low-Power 16-Bit MSP430 MCUs (Rev. D)	PDF	302 KB	28 Mar 2012	3872
Power Management Guide 2012 (Rev. L)	PDF	12.79 MB	09 Feb 2012	23535
Point-of-Load (POL) Power Solutions for Industrial Designs (Rev. A)	PDF	246 KB	03 May 2011	1639
Управление питанием для ULP 16-bit MSP430 MCUs (Rev. A)	PDF	916 KB	22 Mar 2011	682
MSP430 MCUs, Passive RF and Low-Power RF Solutions Guide (Rev. F)	PDF	175 KB	11 Jun 2010	2457

Solution Guides (1)

Title	Abstract	Type	Size (KB)	Date	Views
Industrial Process Measurement and Control Trifold		PDF	827 KB	31 Mar 2008	858

Tools and Software

Name	Part #	Company	Software/Tool Type
ADCPro(TM) Analog-to-Digital Converter Evaluation Software	ADCPRO	Texas Instruments	Application Software
ADS1248 Performance Demonstration Kit	ADS1248EVM-PDK	Texas Instruments	Development Boards/EVMs
Anti-Aliasing Calculation Tool for A to D Converters	ANTIALIASINGCALC	Texas Instruments	Calculation Utilities
CC2520 Evaluation Module Kit	CC2520EMK	Texas Instruments	Development Boards/EVMs
Code Composer Studio (CCStudio) Integrated Development Environment (IDE) v5	CCSTUDIO	Texas Instruments	Code Composer Studio(TM) IDE
MSP430 USB Stick Development Tool	EZ430-F2013	Texas Instruments	Development Boards/EVMs
Op Amp to ADC Circuit Topology Calculator	ADC-INPUT-CALC	Texas Instruments	Calculation Utilities

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